net: accept 64 kB lines in /etc/hosts

Apparently 4 kB is not enough for some people.

Fixes #21674.

Change-Id: If39eeb225d548b578560939f6ce51e31060f5aff
Reviewed-on: https://go-review.googlesource.com/79516
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/parse.go

@@ -69,7 +69,7 @@ func open(name string) (*file, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &file{fd, make([]byte, 0, os.Getpagesize()), false}, nil
+	return &file{fd, make([]byte, 0, 64*1024), false}, nil
 }
 
 func stat(name string) (mtime time.Time, size int64, err error) {